Vehicle digital key system

1. A vehicle digital key system comprising: a first communication module configured to broadcast a first signal at a predetermined time interval, calculate a distance to a key fob based on a second signal corresponding to the first signal when the first communication module receives the second signal from the key fob, and switch a second communication module from a sleep mode to a wakeup mode when the calculated distance is within a preset first threshold; the second communication module configured to switch a plurality of third communication modules from the sleep mode to the wakeup mode and calculate a position of the key fob using at least three third communication modules among the plurality of third communication modules; and a controller configured to unlock a door of a vehicle based on the position of the key fob, wherein the plurality of third communication modules transmit third signals and calculate respective individual distances to the key fob based on fourth signals corresponding to the third signals when the third communication modules receive the fourth signals from the key fob, and the second communication module: selects at least three third communication modules adjacent to each other among the plurality of third communication modules based on the individual distances and calculates the position of the key fob using the individual distances of the selected three third communication modules when the individual distance of the third communication module positioned in a middle among the selected third communication modules is the shortest; and when the individual distance of the third communication module positioned in the middle among the selected third communication modules is not the shortest, calculates the position of the key fob using the individual distances of the selected three third communication modules when the individual distances of selected left and right third communication modules are greater than or equal to a threshold, and reselects third communication modules based on the left third communication module or the right third communication module when the individual distances of the selected left and right third communication modules are smaller than the threshold.

2. The vehicle digital key system of claim 1, wherein the first communication module communicates with the key fob using a frequency of 2.4 [GHz] band, and the second communication module and the third communication modules communicate with the key fob using a baseband frequency and directional antennas.

3. The vehicle digital key system of claim 1, wherein the second signal includes movement speed information about the key fob.

4. The vehicle digital key system of claim 3, wherein the first communication module calculates the distance to the key fob by correcting distance information calculated through a time at which the second signal is transmitted from the key fob and a time at which the second signal is received through a movement speed of the key fob.

5. The vehicle digital key system of claim 4, wherein the first communication module calculates a movement amount of the key fob using the movement speed of the key fob and a time interval between the time at which the second signal is transmitted and the time at which the second signal is received and corrects the distance information by applying the calculated movement amount.

6. The vehicle digital key system of claim 1, wherein the second communication module switches third communication modules other than the selected third communication modules among the plurality of third communication modules to the sleep mode and calculates the position of the key fob based on the fourth signals received by the selected third communication modules.

7. The vehicle digital key system of claim 6, wherein the second communication module: reselects at least three third communication modules using the third communication module having the shortest individual distance from the key fob among the selected three third communication modules; and switches or maintains third communication modules adjacent to left and right sides of the third communication module having the shortest individual distance to the wakeup mode based on the reselecting, and switches or maintains third communication modules other than the third communication module having the shortest individual distance and the third communication modules adjacent to the left and right sides to the sleep mode.

8. The vehicle digital key system of claim 6, wherein the second communication module switches the plurality of third communication modules to the wakeup mode when at least one of the selected third communication modules does not receive the fourth signal.

9. The vehicle digital key system of claim 1, wherein the second communication module communicates with the key fob when the door of the vehicle is closed after being opened, and the controller starts the vehicle based on a result of communication between the second communication module and the key fob and a sensing signal when the sensing signal is received from a sensor disposed in the vehicle.

10. The vehicle digital key system of claim 1, wherein the second communication module: switches the plurality of third communication modules to the wakeup mode when the second communication module communicates with the key fob; and maintains the plurality of third communication modules in the wakeup mode and cuts off start of the vehicle when the fourth signals corresponding to the third signals transmitted by the plurality of third communication modules switched to the wakeup mode are received, and switches the plurality of third communication modules from the wakeup mode to the sleep mode when the fourth signals corresponding to the third signals are not received.

11. A vehicle digital key control method using a vehicle digital key system of a vehicle including a first communication module, a second communication module, and a third communication module, the vehicle digital key control method comprising: broadcasting, by the first communication module, a first signal at a predetermined time interval; calculating, by the first communication module, a distance to a key fob based on a second signal corresponding to the first signal when the first communication module receives the second signal from the key fob; switching, by the first communication module, the second communication module from a sleep mode to a wakeup mode when the calculated distance is within a preset first threshold; switching, by the second communication module, a plurality of third communication modules from the sleep mode to the wakeup mode when the calculated distance is within the preset first threshold; calculating, by the second communication module, a position of the key fob using at least three third communication modules among the plurality of third communication modules; and unlocking, by a controller, a door of the vehicle based on the position of the key fob, wherein the calculating of the position of the key fob includes: transmitting, by the plurality of third communication module, third signals and calculating respective individual distances to the key fob based on fourth signals corresponding to the third signals when the third communication modules receive the fourth signals from the key fob; selecting, by the second communication module, at least three third communication modules adjacent to each other among the plurality of third communication modules based on the individual distances and calculating the position of the key fob using the individual distances of the selected three third communication modules when the individual distance of the third communication module positioned in a middle among the selected third communication modules is the shortest; and when the individual distance of the third communication module positioned in the middle among the selected third communication modules is not the shortest, calculating the position of the key fob using the individual distances of the selected three third communication modules when the individual distances of selected left and right third communication modules are greater than or equal to a threshold, and reselecting third communication modules based on the left third communication module or the right third communication module when the individual distances of the selected left and right third communication modules are smaller than the threshold.

12. The vehicle digital key control method of claim 11, wherein the first communication module communicates with the key fob using a frequency of 2.4 [GHz] band, and the second communication module and the third communication modules communicate with the key fob using a baseband frequency and directional antennas.

13. The vehicle digital key control method of claim 11, wherein the second signal includes movement speed information about the key fob.

14. The vehicle digital key control method of claim 13, wherein the calculating of the distance to the key fob includes calculating the distance to the key fob by correcting distance information calculated through a time at which the second signal is transmitted from the key fob and a time at which the second signal is received through a movement speed of the key fob.

15. The vehicle digital key control method of claim 14, wherein the calculating of the distance to the key fob includes calculating, by the first communication module, a movement amount of the key fob using the movement speed of the key fob and a time interval between the time at which the second signal is transmitted and the time at which the second signal is received and correcting the distance information by applying the calculated movement amount.

16. The vehicle digital key control method of claim 11, wherein the calculating of the position of the key fob includes: switching, by the second communication module, third communication modules other than the selected third communication modules among the plurality of third communication modules to the sleep mode; and calculating, by the second communication module, the position of the key fob based on the fourth signals received by the selected third communication modules.

17. The vehicle digital key control method of claim 16, wherein the calculating of the position of the key fob includes: reselecting, by the second communication module, at least three third communication modules using the third communication module having the shortest individual distance from the key fob among the selected three third communication modules; and switching or maintaining third communication modules adjacent to left and right sides of the third communication module having the shortest individual distance to the wakeup mode based on the reselecting, and switching or maintaining third communication modules other than the third communication module having the shortest individual distance and the third communication modules adjacent to the left and right sides to the sleep mode.

18. The vehicle digital key control method of claim 16, further comprising switching, by the second communication module, the plurality of third communication modules to the wakeup mode when at least one of the selected third communication modules does not receive the fourth signal.

19. The vehicle digital key control method of claim 11, comprising: switching the second communication module from the sleep mode to the wakeup mode when the door of the vehicle is closed after being opened; communicating with the key fob by the second communication module; and starting, by the controller, the vehicle based on a result of communication between the second communication module and the key fob and a sensing signal when the sensing signal is received from a sensor disposed in the vehicle.

20. The vehicle digital key control method of claim 11, further comprising: switching the plurality of third communication modules to the wakeup mode when the second communication module communicates with the key fob; transmitting the third signals by the third communication modules switched to the wakeup mode; and maintaining the plurality of third communication modules in the wakeup mode and cutting off start of the vehicle when the fourth signals corresponding to the third signals are received, and switching the plurality of third communication modules from the wakeup mode to the sleep mode when the fourth signals corresponding to the third signals are not received.